Electrolytic polishing apparatus, electrolytic polishing method, and wafer subject to polishing

ABSTRACT

An electrolytic polishing apparatus for electrolytic-polishing a conductive film subject to formed on a substrate including a resistance measuring unit for measuring the resistance of the film. The electrolytic polishing apparatus may also include a termination point detecting portion for detecting a termination point of polishing by reading a variation of the resistance value measured by the resistance measuring unit, or a polishing control portion for terminating electrolytic polishing on the basis of the termination point of polishing detected by the termination point detecting portion.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to an electrolytic polishing apparatus, anelectrolytic polishing method and a wafer subject to polishing, and morespecifically, to an electrolytic polishing apparatus, an electrolyticpolishing method and a wafer subject to polishing, which permitdetection of a termination point in electrolytic polishing.

[0003] 2. Prior Art

[0004] Copper wiring presents lower electric resistance, lower capacityand higher reliability than aluminum wiring and is thus increasing inimportance for micro elements dominantly affected by circuit delay dueto parasitic resistance and parasitic capacity occurring in the wiring.A damascene method is widely applied as the most popular method offorming copper wiring. In particular, a dual damascene method meets withgeneral acceptance from the viewpoint of manufacturing cost. There isexpectation that a process of manufacturing copper wiring by the use ofthe dual damascene method will be less costly than a conventionalaluminum wiring process.

[0005] However, since chemical mechanical polishing (which will behereinafter referred to as CMP) of copper is considered to be acomplicated process requiring expensive slurry and pad, a problem in anincrease in manufacturing cost is encountered with the CMP. In addition,since the CMP is based on mechanical polishing, not only copperrequiring polishing but also an insulating film around the copper ispolished to bring about erosion, resulting in a problem in difficulty toachieve flatness of a wiring layer. The CMP further finds difficulty indetecting a termination point and therefore presents problems likeover-polishing and under-polishing. As a result, there are problems inthat the CMP causes excessive dishing or inter-wiring short circuit.

[0006] An attempt to form a dual damascene structure by polishing copperby means of electrolytic polishing is now being made for the purpose ofsolving the problems mentioned above.

[0007] On the other hand, in electrolytic polishing, a quantity ofpolishing is decided on the basis of a polishing time. For that reason,an operator finds difficulty in ascertaining a point of time desired toterminate polishing, that is, a termination point of polishing,resulting in problems in that over-polishing or under-polishing occursdepending on variations in thickness of a film subject to polishing,changes in electrolytic polishing conditions or the like.

SUMMARY OF THE INVENTION

[0008] An electrolytic polishing apparatus according to a preferredembodiment of the present invention performs electrolytic polishing of aconductive film subject to polishing formed on a substrate and includesa resistance measuring unit for measuring resistance of the film subjectto polishing. The electrolytic polishing apparatus also includes atermination point detecting portion for detecting a termination point ofpolishing by reading a variation of a resistance value measured by theresistance-measuring unit. The electrolytic polishing apparatus furtherincludes a polishing control portion for terminating electrolyticpolishing on the basis of the termination point of polishing detected bythe termination point detecting portion.

[0009] The electrolytic polishing apparatus includes a resistancemeasuring unit for measuring the resistance of the film subject topolishing, permitting the measurement on the resistance value of thefilm subject to polishing varying with the progress of electrolyticpolishing. That is, with the progress of electrolytic polishing, thethickness of the film subject to polishing is made smaller, andaccordingly, the resistance value measured by the resistance measuringunit increases. When the film subject to polishing is completely removedby polishing, the resistance measuring unit proceeds a measurement of aresistance value of the substrate on which the film subject to polishingis formed, for instance, and as a result, the resistance value reaches aconstant reaches a constant value.

[0010] The electrolytic polishing apparatus detects the terminationpoint of polishing by reading the variation of the resistance value ofthe film as described the above with the termination point detectingportion. For instance, a point of time when the resistance value reachesa constant value is detected as the termination point of polishing.

[0011] Then, the electrolytic polishing apparatus terminateselectrolytic polishing immediately after the termination point ofpolishing is detected. A process between detection of the terminationpoint of polishing and termination of electrolytic polishing may beautomatically performed by using the polishing control portion toterminate electrolytic polishing on the basis of detection of thetermination point of polishing.

[0012] An electrolytic polishing method according another preferredembodiment of the present invention performs electrolytic polishing of aconductive film subject to polishing formed on a substrate and includesthe step of detecting a termination point of electrolytic polishing toterminate electrolytic polishing by detecting a variation of electricresistance of the film subject to polishing in the process ofelectrolytic polishing.

[0013] The electrolytic polishing method detects the variation ofresistance of the film subject to polishing in the process ofelectrolytic polishing. That is, with the progress of electrolyticpolishing, the thickness of the film subject to polishing is madesmaller, and accordingly, the resistance of the film subject increases.When the film is completely electrolytic-polished, the electrolyticpolishing method proceeds to measure of a resistance value of thesubstrate on which the film subject to polishing is formed, forinstance, and as a result, the resistance value reaches a constantvalue. For instance, the time when the measured resistance value reachesa constant value is set as the termination point of polishing. Theelectrolytic polishing method permits accurate detection of thetermination point of electrolytic polishing to terminate electrolyticpolishing by detecting the variation of resistance of the film subjectto polishing as described the above.

[0014] A wafer subject to polishing according to another preferredembodiment of the present invention includes a substrate, a firstconductive layer formed on the surface of the substrate, a terminalconnection area connected with terminals of a resistance measuring unitand formed on the surface-side periphery of the first conductive layerand a second conductive layer subjected to electrolytic-polishingselectively to the first conductive layer and formed on the surface ofthe first conductive layer except for the terminal connection area.

[0015] According to the wafer subject to polishing, since the terminalconnection area is formed on a surface-side periphery of a firstconductive layer, a resistance varying according to polishing of asecond conductive layer can be measured by, for instance, connecting theterminals of the resistance measurement unit to the portions of theterminal connection area facing each other within a plane of the wafersubject to polishing. Then, when the second conductive layer is removedby means of electrolytic polishing, the thickness of the conductivelayer portion is reduced, and accordingly, the measured resistance valueincreases. When the second conductive layer is completely removed fromthe first conductive layer by means of electrolytic polishing, theresistance measuring unit proceeds to measure only the resistance of thefirst conductive layer, and as a result, the resistance value reaches anapproximately constant value, regardless of the continuation ofelectrolytic polishing. For instance, a period of time when theresistance value reaches a constant value is set as the terminationpoint of electrolytic polishing of the second conductive layer,resulting in detection of the termination point of electrolyticpolishing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The foregoing and other objects and features of the inventionwill become apparent from the following description of the embodimentsof the invention with reference to the accompanying drawings, in which:

[0017]FIG. 1 is a schematic view showing an embodiment of anelectrolytic polishing apparatus, according to a preferred embodiment ofthe present invention;

[0018]FIG. 2 is a schematic view showing another constitution of aresistance measuring unit, according to a preferred embodiment of thepresent invention;

[0019]FIG. 3 is a sectional view showing an schematic structure of awafer subject to electrolytic polishing, according to a preferredembodiment of the present invention;

[0020]FIG. 4 is a graphic representation showing a relation betweenresistance value and an electrolytic polishing time, according to apreferred embodiment of the present invention;

[0021]FIG. 5 is a sectional view showing a schematic structure forconnection of a termination point of electrolytic polishing, accordingto a preferred embodiment of the present invention; and

[0022]FIG. 6 is a sectional view showing a schematic structure of anembodiment of a wafer subject to polishing, according to a preferredembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] A description will now be given of an embodiment of anelectrolytic polishing apparatus according to the present invention withreference to FIG. 1.

[0024] As shown in FIG. 1, an electrolytic polishing apparatus 1 forelectrolytic-polishing a conductive film (not shown) formed on asubstrate has a cup 11 for holding an electrolytic polishing solution.In the electrolytic polishing apparatus 1, electrolytic polishing iscarried out on a condition on which a wafer 51 having a film subject topolishing (not shown) made of a conductive material is used as anode.Thus, the electrolytic polishing apparatus 1 has a plurality ofelectrodes 12 connected, for instance, to a surface-side periphery ofthe wafer 51 as for supplying current to the wafer 51.

[0025] The wafer 51 has the film subject to polishing on a conductivefilm (not shown) formed on the substrate, for instance, and theconductive film is exposed to the outside through the surface-sideperipheral portion of the wafer 51. Each electrode 12 is connected tothe conductive film exposed to the outside. The electrodes 12 areprovided at a predetermined interval, for instance, on an annularinsulator 13 of a size as large as the outer periphery of the wafer 51.Rubber is used for the insulator 13, for instance.

[0026] The electrolytic polishing apparatus 1 also has a resistancemeasuring/measurement unit 21 for measuring the resistance of theconductive film formed on the wafer 51. Terminals 22, 23 of theresistance measuring unit 21 are connected to portions of the electrodes12. The positions of the electrodes connected to the terminals of theresistance measuring unit 21 are opposite to each other through the cup11. In addition, the terminals 22, 23 of the resistance measuring unit21 can also be connected to the conductive film communicating with thefilm subject to polishing of the wafer 51 at positions opposite to eachother through the cup 11, instead of the electrodes 12. A plurality ofpairs of terminals are also applicable for connection of the resistancemeasuring unit 21 to the electrodes 12 without being limited to a pairof terminals like the terminals 22, 23 of the resistance measuring unit21. Non-uniformity in a plane of the wafer 51 is measured by connectingthe plurality of pairs of terminals, permitting highly accuratedetection of a termination point of electrolytic polishing.

[0027] A tester may be used for the resistance measuring unit 21 tomeasure the resistance. As shown in FIG. 2, for instance, the resistancemeasuring unit 21 may be composed of an ampere meter 25 for measuringcurrent and a voltmeter 27 for measuring voltage so as to calculatingthe resistance on the basis of the measured current and voltage.

[0028] As shown in FIGS. 1 and 2, the resistance measuring unit 21 hasfurther a termination point detecting portion 31 for detecting atermination point of polishing by reading a variation of the measuredresistance value. The resistance measuring unit 21 further has apolishing control portion 33 for terminating electrolytic polishing onthe basis of the termination point of polishing detected by thetermination point detecting portion 31.

[0029] The electrolytic polishing apparatus 1 has the resistancemeasuring unit 21 for measuring the resistance of the film subject topolishing, permitting the measurement of the resistance value of thefilm subject to polishing varying according to progress of electrolyticpolishing. That is, with the progress of electrolytic polishing, thethickness of the film subject to polishing is reduced, and accordingly,the resistance value measured by the resistance measuring unit 21increases. When the film subject to polishing is completely removed bypolishing, the resistance measuring unit 21 proceeds to measure aresistance value of the conductive film on which the film subject topolishing is formed and, as a result, the resistance value reaches aconstant value.

[0030] The electrolytic polishing apparatus 1 detects the terminationpoint of polishing by reading the variation of the resistance value ofthe film subject to polishing with the termination point detectingportion 31. For instance, a point when the resistance value reaches aconstant value is determined as the termination point of polishing.

[0031] The electrolytic polishing apparatus 1 terminates electrolyticpolishing immediately after the termination point of polishing isdetected. A process between detection of the termination point ofpolishing and termination of electrolytic polishing may be performedautomatically by using the polishing control portion 33 to terminateelectrolytic polishing on the basis of detection of the terminationpoint of polishing.

[0032] A description will now be given of an embodiment of anelectrolytic polishing method according to the present invention withreference to FIGS. 3 and 4.

[0033] The wafer 51 has a first conductive film 53 formed on a substrate52 and a second conductive film 54 formed as a film subject to polishingon the first conductive film 53, as shown in FIG. 3. A description willnow be given of a method of electrolytic-polishing the film subject topolishing. The second conductive film 54 brought into contact with anelectrolytic polishing solution (not shown) is subjected to electrolyticpolishing under a lapse of time, so that the thickness of the secondconductive film 54 is made smaller. The electrolytic polishing method isby detecting the termination point of electrolytic polishing toterminate electrolytic polishing by detecting a variation of theresistance of the second conductive film (the film subject to polishing)in the process of electrolytic polishing.

[0034] A description will now be given of electrolytic polishing in adamascene process for forming copper wiring. A barrier metal layer isformed as the first conductive film 53 on the substrate 52, and a copperfilm is formed as the second conductive film 54 on the surface of thebarrier metal layer. With the progress of copper electrolytic polishing,the thickness of the copper film on a flat surface is reduced. With areduction in film thickness, electric conduction becomes dependent onlyon the barrier metal layer left on a substratum of the copper film andan extremely thin copper film. As a result, a resistance value measuredby the resistance measuring unit becomes abruptly increased with theprogress of electrolytic polishing as shown in FIG. 4. The rise of theresistance value means that there is little left of a copper film on aflat portion. After going through the rise of the resistance value, themeasured resistance value reaches a constant value. The resistance valuemeasured in this place is considered to be a resistance value of thebarrier metal, which is formed on the substratum of the copper film.Since the barrier metal layer is not subjected to electrolyticpolishing, the resistance of wiring reaches a constant value.

[0035] Incidentally, the measurement of the resistance value can be alsodone by monitoring plating current and voltage applied from an electrodefor electrolytic polishing to a facing electrode through the copperfilm/barrier metal layer. A plurality of pairs of electrodes are alsoapplicable as the electrodes for measurement of the resistance valuewithout being limited to a pair of electrodes. For instance, theplurality of pairs of electrodes may be installed for the measurement ofnon-uniformity in the plane of the wafer, permitting more highlyaccurate detection of the termination point of electrolytic polishing.

[0036] Copper electrolytic polishing may be set to bring to stopaccording to circumstances such as a case of over-polishing a copperfilm 64 intentionally to form a recess portion 65 in a groove 62 formedin an insulating film 61 through a barrier metal layer 63 as shown inFIG. 5 (1), and a case of just-polishing the copper film 64 to bury thecopper film 64 in the groove 62 formed in the insulating film 61 throughthe barrier metal layer 63 so as to be flush with a flat surface S asshown in FIG. 5 (2).

[0037] Control of a stop point at which electrolytic polishing isstopped can be performed accurately on the basis of the measurement onthe variation of the resistance as shown in FIG. 4. As a result, adifficulty in detection of the termination point as the problemsencountered with the conventional electrolytic polishing or CMP may besolved, permitting the termination of polishing at a desired polishingcondition. An electrolytic polishing system may detect automatically thetermination point of polishing to stop polishing by setting feedback forstopping electrolytic polishing when the resistance value reaches anapproximately constant value. Incidentally, an operator may alsoterminate electrolytic polishing after making judgment on thetermination point of polishing by reading the variation of the measuredresistance value.

[0038] An electrolytic polishing method is performed by detecting thevariation of the resistance of the film subject to polishing in theprocess of electrolytic polishing. That is, with the progress ofelectrolytic polishing, the thickness of the film subject to polishingis made smaller, and accordingly, the resistance of the film subject topolishing increases. When the film subject to polishing is thoroughlypolished, the electrolytic polishing method proceeds to measure theresistance value of the substrate on whiche the film subject topolishing is formed, for instance, and the resistance value reaches aconstant value. For instance, a point of time when the measuredresistance value reaches a constant or approximately constant value isset as the termination point of polishing. The electrolytic polishingmethod permits accurate detection of the termination point ofelectrolytic polishing to terminate electrolytic polishing by detectingthe variation of the resistance of the film subject to polishing asdescribed the above.

[0039] A description will now be given of an embodiment of a wafersubject to polishing according to the present invention with referenceto a sectional view of FIG. 6.

[0040] As shown in FIG. 6, a wafer 71 subject to polishing (equivalentto the wafer 51 mentioned above) has a substrate 72, a first conductivelayer 73 formed on a surface of the substrate 72, a terminal connectionarea 73 a connected with the terminals 22, 23 of the resistancemeasuring unit and formed on the surface-side periphery of the firstconductive layer 73 and a second conductive layer 74 subjected toelectrolytic-polishing selectively to the first conductive layer 73 andformed on the surface of the first conductive layer 73 except for theterminal connection area 73 a.

[0041] Since the wafer 71 subject to polishing has the terminalconnection area 73 a on the surface-side periphery of the firstconductive layer 73, the resistance value of the film subject topolishing (the first and second conductive layers 73, 74, practically)varying according as the second conductive layer 74 iselectrolytic-polished may be measured by connecting the terminals 22, 23of the resistance measuring unit to the terminal connection areaportions 73 a facing each other in the plane of the wafer subject topolishing 71, for instance. When the second conductive layer 74 isremoved by means of electrolytic polishing, the thickness of theconductive layer portion is reduced, and therefore, the measuredresistance value increases. When the second conductive layer 74 iscompletely removed from the first conductive layer 73 by means ofelectrolytic polishing, the resistance measuring unit (not shown)proceeds to measure only the resistance of the first conductive layer73, and the resistance value reaches an approximately constant valueregardless of the continuation of electrolytic polishing. For instance,this point of time when the resistance value reaches a constant value isset as a termination point of electrolytic polishing of the secondconductive layer 74, resulting in detection of the termination point ofelectrolytic polishing.

[0042] As has been described in the foregoing, the electrolyticpolishing apparatus according to the present invention includes theresistance measuring unit for measuring the resistance of the filmsubject to polishing, permitting the measurement on the resistance valueof the film subject to polishing varying with the progress ofelectrolytic polishing. Thus, the electrolytic polishing apparatus maydetect the termination point of polishing by reading the variation ofthe resistance value of the film subject to polishing varying with theprogress of electrolytic polishing. Further, the process betweendetection of the termination point of polishing and termination ofelectrolytic polishing can be automatically performed by using thepolishing control portion to terminate electrolytic polishing on thebasis of detection of the termination point of polishing. Thus, theelectrolytic polishing apparatus of the present invention permits highlyaccurate electrolytic polishing.

[0043] The electrolytic polishing method of the present invention isperformed by detecting the variation of resistance of the film subjectto polishing in the process of electrolytic polishing, permittingaccurate detection of the termination point of electrolytic polishing toterminate electrolytic polishing by reading the variation of theresistance value. Thus, the electrolytic polishing method of the presentinvention permits highly accurate electrolytic polishing.

[0044] Since the wafer subject to polishing of the present invention hasthe terminal connection area on the surface-side periphery of the firstconductive layer, the resistance value of the film subject to polishingvarying according to the electrolytic polishing of the second conductivelayer can be measured by connecting the terminals of the resistancemeasuring unit to the terminal connection area portions facing eachother in the plane of the wafer subject to polishing, for instance. Thewafer subject to polishing on which measurement of the variation of theresistance value thereof in the process of electrolytic polishing can beused for detecting the termination point of polishing accurately toterminate electrolytic polishing. Thus, the wafer subject to polishingof the present invention permits highly accurate electrolytic polishing.

[0045] Finally, the configurations and structures of respective unitsand portions described specifically with respect to the preferredembodiments of the present invention are only examples of realization ofthe present invention, so the embodiments thereof should not beconstrued as to limiting the technical scope of the present invention.

[0046] Accordingly, the present invention is not limited to thepreferred embodiments described above, thus any variation as well as anycombination and/or sub combination of the embodiments is permitted,without departing from the scope of the present invention.

[0047] For example, although the polishing method described above isdone based on an electrolytic polishing apparatus and method, it is notlimited to such type of polishing. Also, any kind or method ofmeasurement can be applicable to the present invention, provided thatmeasurement of electric resistance of the barrier layer combined withthe layer to be polished is measured so as to establish the terminatingpoint of polishing.

1. (Canceled)
 2. An electrolytic polishing apparatus forelectrolytic-polishing a conductive film formed on a substrate,comprising: a resistance measuring unit for measuring electricresistance of said conductive film and a etching stopper film formed onsaid substrate, and further comprising a termination point detectingunit for detecting a termination point of polishing by reading avariation resistance value of said conductive film and said etchingstopper film measured by said resistance measuring unit.
 3. (Canceled)4. (Canceled)
 5. (Canceled)
 6. (Canceled)
 7. (Canceled)
 8. (Canceled) 9.(Canceled)
 10. (Canceled)